1. Field of the Invention
This invention relates to steer-by-wire systems, and more particularly to use of a torque sensor to steer a vehicle that includes a steer-by-wire system.
2. Description of the Related Art
Steer-by-wire systems have been used in aircraft applications for many years to provide an electronic connection between a yoke controlled by the pilot and tail flaps, wing flaps and other devices used to maneuver the aircraft. In recent years, steer-by-wire systems have also been applied to land-based vehicles.
Land-based vehicles typically have a steering wheel to control the direction of the vehicle and wheels to allow movement of the vehicle. Steer-by-wire systems in land-based vehicles are characterized by a lack of direct mechanical linkage between the steering wheel and the wheels controlled by the steering wheel. In place of the mechanical linkage, actuators are used to control a turning angle of the wheels. In general, a controller controls the turning angle of the wheels as a function of the angular position of the steering wheel. The angular position of the steering wheel is provided as an electric signal to the controller by a steering sensor.
The steer-by-wire systems of land-based vehicles may also include feedback to the driver of the vehicle. In general, the feedback simulates the conventional mechanical linkage to the wheels by providing stability and xe2x80x9croad feelxe2x80x9d to the steering wheel. The feedback is provided by a controlled resistive force capable of supplying varying amounts of counter-torque to the steering wheel. The control system for the varying amounts of counter-torque includes a torque sensor to sense the torque applied to the steering wheel by the driver. A steer-by-wire system that includes many of the previously described features is disclosed in U.S. Pat. No. 6,138,788 to Bohner et al.
A general concern in steer-by-wire systems for land-based vehicles is failures within the system that prohibit control of the wheels with the steering wheel. Solutions to this concern may include the use of backup mechanical linkage systems or backup hydraulic systems. Another prior art solution may involve the installation of redundant components in the vehicle for the steer-by-wire system. Upon failure of the primary components, the redundant components may be used.
A known problem with these prior art solutions is additional complexity of the associated vehicle as well as added cost due to additional hardware. In addition, the backup or redundant components require additional space and add weight to the vehicle. Further, the additional components may increase the electrical or mechanical energy supply requirements of the vehicle.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the embodiments described below include a method and system for operating a vehicle during a failure in a steer-by-wire system. The method and system allows an operator to steer the vehicle with the steer-by-wire system during the failure using a torque sensor.
The steer-by-wire system comprises a steering actuation system, a controller and a driver interface system. The steering actuation system is directed by the controller, as a function of the driver interface system, to maneuver the vehicle. The driver interface system allows the operator control of the operation of the steer-by-wire system.
The driver interface system includes a steering mechanism, a steering mechanism position sensor and a torque sensor. The steering mechanism may be moved by the operator to steer the vehicle. The position of the steering mechanism, as measured by the steering mechanism position sensor, may be used by the controller to direct the steering actuation system. The torque measured by the torque sensor is indicative of the amount of force applied to the steering mechanism by the operator. A dynamic relationship exists between the applied torque and the resulting position of the steering mechanism.
When a failure occurs in the driver interface system, the controller may restrict or eliminate movement of the steering mechanism by the operator. By controlling movement of the steering mechanism, the controller may direct the steering actuation system as a function of the torque sensor instead of the steering mechanism position sensor. The controller uses the magnitude and direction of torque applied by the operator to the steering mechanism to represent the operator""s intent to steer the vehicle. The controller may use the torque to estimate what the position of the steering mechanism would otherwise be and direct the steering actuation system accordingly.
Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.